Computing devices have packages that are conventionally rectangular in outer shape. These computing devices also have a conventional group of hardware devices, including a hard drive storing an operating system and driver files for the specific hardware of the computer, ports and removable media.
Similarly, some peripherals for a computer have historically been rectangular, such as keyboards, displays, and other such devices. Therefore, portable computers have conventionally been made in rectangular shapes also.
A computer conventionally has certain characteristics, that are constant for the computer itself, not for the user that is using the computer. If the computer is sold or used by another user, it keeps the same characteristics.